Since third generation (3G) mobile communication technology was developed, packet data services have been greatly in demand. In particular, the packet data has a very large variation in data rate and has a very large data rate in comparison with conventional data. Thus, the demands for efficiently transmitting the packet data have highly increased.
To meet such demands, orthogonal frequency-division multiplexing (OFDM) technology transmits data by dividing a frequency band into a plurality of sub-carrier frequencies and allocating the appropriate number of data bits for sub-carriers. As such, the data rate is improved by dividing temporally sequential data into certain temporal units, converting the temporal units to be parallel to each other, and transmitting a subcarrier which is carrying each of the temporal units. Furthermore, temporal discontinuity may be achieved by transmitting sequential data in parallel and thus efficient scheduling may be obtained in the packet data having a very large variation in data rate.
Meanwhile, in a communication system, the data rate and the variation in data rate are variably changed. Thus, allocating fixed resources is very inefficient in view of transmission efficiency. Accordingly, the transmission efficiency may be improved by variably changing the data rate of the packet data in accordance with the amount of data to be transmitted or the state of a channel medium for communication. However, although the above-described method of variably changing the data rate may improve the transmission efficiency, control information of variably changing data has to be informed whenever the data is changed. Therefore, an efficient method of transmitting variably changing control information is required.
Conventionally, the packet data is transmitted in a downlink by using a high-speed downlink packet access (HSDPA) method referred to as a third generation partnership project 2 (3GPP2) 1x evolution-data optimized (1xEV-DO) method or a third generation partnership project (3GPP) release-5 method, and a mobile worldwide interoperability for microwave access (WIMAX) method referred to as a wireless broadband (WiBRO) method in accordance with the Institute of Electrical and Electronics Engineers (IEEE) 802.16e.
In the 3GPP2 1xEV-DO method, by transmitting data rate control (DRC) information together with packet data to a temporal slot designated as a downlink, information regarding the packet data in the downlink is transferred. A mobile station receives the DRC information and thus may correctly receive the packet data by checking the information regarding the packet data.
In the HSDPA method, the transmission efficiency is improved by transmitting the packet data with a certain time interval after transmitting information regarding a modulation method, an allocated orthogonal variable spreading factor (OVSF) channel, the data rate of the packet data in a downlink through high speed-shared control channels (HS-SCCHs). Here, the HS-SCCHs are common channels to be checked by all mobile stations and the number of channels is fixed to be four. The mobile stations check whether corresponding control information is transmitted through the four HS-SCCHs.